Excretion CAPE Biology Unit 2

What is Excretion?  Excretion is the process by which waste products of metabolism and other non- useful substances are eliminated from an organism

 The elimination of waste products by an organism, that results from metabolic processes. In plants, waste is minimal and is eliminated primarily by diffusion to the outside environment.  Animals have specific organs of excretion. In vertebrates, the kidney filters blood, conserving water and producing urea and other waste products in the form of urine.

What is Osmoregulation?  Osmoregulation is the physiological processes that an organism uses to maintain water balance; that is, to compensate for water loss, avoid excess water gain, and maintain the proper osmotic concentration (osmolarity) of the body fluids.

 Most humans are about 55 to 60 percent water by weight (45 percent in elderly and obese people and up to 75 percent in newborn ). Many jellyfish are 95 percent or more water.  Another definition of osmoregulation is: The process by which the water content and the ion concentration is regulated and kept constant in the cells.

The need to remove nitrogenous waste from the body  Perhaps the most troublesome by-product of metabolism is nitrogen-containing waste. Nitrogen is removed from proteins and nucleic acids when they are broken down for energy or converted to carbohydrates and/or fats. The nitrogenous waste product is Ammonia. This is a very small, but very toxic by- product of the metabolic removal of nitrogen from proteins and nucleic acids.

 The human body cannot utilize the Ammonia; therefore it has to be excreted before its toxic properties damage the body.

 The two physiological processes, excretion and osmoregulation are interconnected as they both are responsible for bringing about homeostasis in the body. The physiological mechanisms involved are intimately bound with each other, so much so, in higher vertebrates like mammals, kidneys perform functions, excretion and osmoregulation.

 Excretion gets rid of the waste in or body. For this to work, the waste, especially nitrogenous waste, has to be diluted into the blood stream so that is may be transported to the kidneys. The water from the blood is used-up to facilitate the diffusion of the waste to the blood stream.

 Osmoregulation is now “activated” and then replenishes the water content of the blood. This water comes from the kidneys, as it extracts the excess water and waste from the blood stream. Osmoregulation is a homeostatic mechanism. It is activated when the body recognises that it is lacking in water or essential ions, or there is too much in the blood stream.

Major excretory products of Animals and Plants  Nitrogenous compounds such as urea, uric acid and ammonia (these come from the breakdown of proteins, nucleic acids and excess amino acids)  Oxygen from photosynthesis in plants-some of this may be used in respiration  Carbon dioxide from cellular respiration in autotrophic organisms  Bile pigments from the breakdown of ‘heam’ in the liver

Excretory structures in Animals  THE KIDNEYS : Has many functions. It servers essential regulatory roles in most animals. They are essential in the urinary system, and serves haemolytic functions in maintaining the blood pressure by maintaining salt and water balance, etc.  Ureter : Tubular structure that carries urine from kidneys to bladder

 Urinary Bladder : Stores and releases urine  Urethra : Excretes urine from bladder to the outside of the body  Skin : Excretes water, sodium chloride, and urea.  Lungs : expels useless gasses.

Deamination  Deamination is the removal of an amine group from a molecule. Enzymes which catalyse this reaction are called deaminases.  In the human body, deamination takes place primarily in the liver, however glutamate is also deaminated in the kidneys. Deamination is the process by which amino acids are broken down if there is an excess of protein intake. The amino group is removed from the amino acid and converted to ammonia. The rest of the amino acid is made up of mostly carbon and hydrogen, and is recycled or oxidized for energy.